Siemens 5SY6403-8 SENTRON MCB — 4-pole D-curve, 3 A, 30 kA
The Siemens 5SY6403-8 is a SENTRON 5SY6 series miniature circuit breaker (MCB) with a D tripping characteristic, 4 poles (4P), rated at 3 A at 400 V AC, 50/60 Hz. It carries a 30 kA breaking capacity per IEC 60947-2 and 6 kA per EN 60898, with a UL 1077 rating of 5 kA.
That's a full industrial-grade rating, not the residential 6 kA from EN 60898. The D-curve trips magnetically between 10× and 20× In (30–60 A for this 3 A unit), so it's sized for motor feeders or transformers where the start-up surge would otherwise pop a B or C curve. That covers most 48 V and 60 V DC control circuits found in industrial automation, but not 110 V DC battery banks. The multi-phase AC rating goes to 440 V, so it's fine on 400 V three-phase systems with a slight headroom. Temperature range is -40 to 75 °C, with derating on humidity above 55 °C. That's wide enough for unheated enclosures in northern climates or near process heat.
Mounts via the quick-assembly system — snap-on to DIN rail, any position. Width is 72 mm (4 width units at 18 mm each), depth 76 mm, installation depth 70 mm.